This invention was made in the course of, or under, a contract with the Energy Research and Development Administration. It relates in general to molten salt batteries and, in particular, to batteries having molten chloroaluminate solvents and cathodes comprising positive oxidation states of sulfur. Such a battery is described in commonly assigned U.S. Pat. No. 3,966,491 for "Molten Salt Electrochemical Systems for Battery Applications" issued June 29, 1976 to Gleb Mamantov, Roberto Marassi, and James Q. Chambers, the disclosure of which is herein incorporated by reference.
The battery described in U.S. Pat. No. 3,966,491 comprised a cathode of sulfur having a positive oxidation state of +1 or less. It was therein disclosed that the molten salt electrolyte for both cathode and anode compartments was a mixture of AlCl.sub.3 /NaCl having a mole ratio of from 49/51 to 80/20. In a specific example, the electrolyte comprised a salt mixture of AlCl.sub.3 /NaCl mole ratio of 49.8/50.2, the cathode compartment containing 0.5 gram of sulfur. The cell was charged by anodizing a tungsten or carbon charge collector in the cathode compartment. The potential measured relative to an external aluminum reference rose from 1.1 to 2.2 volts during charging. A significant improvement in such a battery would be achieved if sulfur could be oxidized to a higher oxidation state than +1, thereby resulting in a higher power/weight ratio. A molten salt concentration cell with aluminum electrodes is described in U.S. Pat. No. 3,770,503 to Brabson et al.